This invention relates to a refractive optical deflector for use in optical scanning and other applications.
There are two fundamental types of optical scanning: these are input scanning and output scanning.
Input scanning occurs when an existing image, such as on celluloid film or paper, forms a target image. The target image is illuminated and electromagnetic radiation, such as light, reflected from or transmitted through the target image is scanned into a machine and then digitised. Common examples include facsimile machines and scanners attached to computers.
Output scanning is the reverse of input scanning. In the case of output scanning a target object in the form of a light-sensitive film plate, light-sensitive paper sheet, or other radiation sensitive device, is exposed to a highly focussed and modulated radiation (light) source which traverses, or scans, the target object thereby imprinting an image onto the target.
Conventional technology for exposing an image on a light-sensitive plate in output scanning begins with a light source, such as a laser or a light-emitting diode capable of emitting a fine collimated beam. In the case where the image is required to be of high quality, the laser beam is first expanded through a beam expander and is subsequently reflected off a rotating, or oscillating, beam deflector, such as a rotating polygon or a galvanometer deflector. The deflector causes the beam to scan along an image plane, albeit with a radial focal plane. Finally, the beam is generally passed through a telecentric field-flattening lens, or a special lens known as an F-theta lens, which focusses the light onto a flat focal plane by extending the focal length towards the periphery of the scan.
There are several ways in which input scanning can be effected to scan a target image into a computer or the like. Where high resolution imaging is required, a typical input scanner employs a laser as a radiation (light) source. Indeed, for three-colour imaging three lasers of different frequencies may be used. In the case of a drum scanner, a target image in the form of a film or the like is mounted on a cylindrical drum which is rotated about its axis. The lasers remain fixed with their beams focussed on the target film. The rotating (or spinning) drum avoids the need for a deflector mechanism. As the laser light passes through the film, the intensity of the beam is attenuated according to the opacity of the film and the transmitted beam is detected by stationary detectors, such as photodiodes. The output from the detectors is digitised and transmitted to the computer.
It is a disadvantage of known input and output scanners that the optical deflectors they incorporate require a substantial number of optical and mechanical components which give rise to undesired complexity and degraded optical performance.
It is therefore an object of the present invention to provide an optical deflector which overcomes or at least reduces the disadvantages of known deflectors.